IGPP is pleased to invite you to join its Winter 2023 Seminar Series presentation featuring Caltech's Jeffrey Park. Dr. Park's talk, "The Green Dog That Did Not Bark: Mid-Ocean Hotspots, Seismic Anisotropy and Underplated Crust" will occur at 12pm May 30, 2023 over Zoom: https://ucsd.zoom.us/j/96543104805?pwd=NTVVVVovRHpqSGhHbEhpbm1ZYmd0QT09 Password: igpp
Time: 12:00 pm, Pacific Time
Location: Revelle conference room, and Zoom
Abstract: Active-source marine-refraction deployments and teleseismic receiver functions, across diverse mid-ocean hotspot systems, find evidence for a 7-10-km layer beneath the oceanic crust, often interpreted as magmatic underplating of the oceanic Moho by plutonic rock of intermediate wavespeeds. High-frequency receiver functions at two long-running seismic observatories at mid-Pacific hotspot islands reveal this underplating to be multilayered and anisotropic within ~30 km of the island summits. Magmatic underplating predicts several processes and features, such as shallow seismic activity and a ring of raised topography, that are not observed at hotspot islands, but are matched by similar geologic processes at the Yellowstone hotspot and in the coronae of Venus. An alternate hypothesis for mid-ocean islands is “metasomatic underplating” whereby crustal fractures develop during magma ascent to allow seawater to infiltrate and to serpentinize the sub-Moho mantle. The metasomatic-underplating hypothesis posits that serpentinization of the sub-Moho mantle sustains fluid ingress via volume expansion during olivine hydration. The metasomatic hypothesis is speculative, but one can assess its broader impacts and form testable predictions. If seawater penetrates the oceanic crust as a byproduct of hotspot volcanism, exchanging seawater carbonate for silica, and carries this silica deeper to serpentinize the uppermost mantle, a surprising collection of geophysical and geochemical observations can potentially be explained. On a larger scale, metasomatized crust and mantle beneath hotspot tracks would become buoyant ribbons trapped within cool dense slabs and are likely avenues for water and CO2 to reach Earth’s mantle transition zone.